The present invention relates generally to ball threads, and more particularly to a ball thread having a flange for fitting to machinery, apparatus or the like.
Since ball threads are less frictional and highly efficient, they are employed in various measuring instruments, medical appliances, computer terminals and the like, to say nothing of industrial robots.
FIG. 8 is a sectional view of the principal part of a ball thread heretofore in use. The ball thread comprises a threaded shaft 1, a nut 2 fitted over the threaded shaft 1 with the internal and external threads of the respective parts aligned in the same position, balls 3 inserted into the groove formed by a combination of the threads in the threaded shaft 1 and the nut 2, and a return groove 4 fitted to the nut 2 so that the balls 3 are made movable therethrough. At one end of the nut 2 is a flange 5 having a flange face 5a perpendicular to the axis of the threaded shaft 1 and bolt holes for use in fitting the ball thread to machinery, apparatus or the like 6 (portions where the ball thread is fitted to machinery or apparatus), whereby the flange 5 can be fitted to machinery, apparatus or the like 6 by means of fixing screws 7.
The aforesaid ball thread with the flange is constructed such that, when an apparatus 6, for example, is moved along the threaded shaft 1 while both ends thereof are fixed, the nut 2 screwed onto the threaded shaft 1 and secured to the apparatus 6 by means of the flange 5 causes the apparatus 6 to be revolved as it moves along the threaded shaft 1.
Conversely, with the ball thread fitted to the apparatus 6 via the flange 5 and with the revolution of the apparatus 6 kept under control it is possible to move the apparatus 6 in the axial direction of the shaft when the threaded shaft 1 is rotated by a motor.
Unlike a ball thread without a flange, the ball thread having the flange is capable of simplifying and quickening the work of fitting the ball thread to the apparatus. However, it is not always easy to align the threaded shaft perpendicularly to the fitting surface of the flange for keeping the apparatus in proper position. When the flange is fitted to the apparatus, however, mill scales will have to be removed therefrom to smooth the surface, if the apparatus is carrying such mill scales because it has not yet been subjected to surface finish. When the mill scales are not removed, a shim is put between the flange-fitting surface of the apparatus and the flange to secure the perpendicularity of the threaded shaft to the former.
Particularly when the apparatus is fitted via the flange to the threaded shaft of the ball thread at an angle with the latter, the fitting work will take much time and less accurate will typically resulting arrangement.
Such fitting work requires more manhours and, as it includes operations performed by trial and error, improvements to increase the accuracy and efficiency of such fitting are still desired.
Regarding a similar problem arising from fitting a linear ball bearing to machinery, apparatus or the like, the present applicant discloses a technique of making the ball bearing unit movable, particularly making it capable of swiveling with respect to a flange unit (U.S. Pat. No. 5,230,567) so as to solve the problems as stated above. However, only making the ball bearing unit of such a ball thread movable with respect to the flange still falls short of accomplishing the intended purpose because the nut is moved back and forth by utilizing the rotation of the threaded shaft.